Distinguishing between READ and WRITE synchronized?
Example: highly multi-threaded application, but almost all threads use a common resource - read only in most cases.
In some rare cases (few in number and occurrence), however, the resource can be modified by a single thread. So the resource has to be synchronized, with the result that only one thread can be running at the same time.
Idea (stolen from data base systems...): Why not introduce something like a "weakSynchronized" in the Java standard, such that as many "weakSynchronized" blocks as there are can aquire the monitor on the resource at the same time without blocking each other. A normal "synchronized" then would have to work as follows: not allow any new "weadSynchronized" blocks to access the monitor (for not having to wait eternally), and then wait until all old "weakSynchronized" blocks release the resource.
What about this idea?
Background: Currently worked with such an application - decision was to use the good old synchronized for having easy code and not having to implement an own mechanism - but this way, the application is not as fast as it could be (was faster, but with deadlocks, when synchronization was not yet correct).
Seems so - obviuosly the java stuff had this idea just a little before me.
Quite firm to java 1.4, but seems as if I still have to learn for 1.5...
I'll have a look for that.
Similar Messages
-
Why is my SSD showing 250mb/s difference between read and write...
So i have recently upgraded to a SSD in my 2011 MBP. 2.4Ghz i5 16Gb RAM. I swapped my HDD with a Samsung 840 Series 250Gb SSD, I noticed a huge speed bump. See attached photos. Read is clocked at 503MB/s peak, and Write is clocked at 260MB/s peak on the SSD. My Question is why is there a 250MB/s difference between read and write?? Using Black Magic Disk Speed test. Mac OS X 10.8.4 Beta.
ThanksWrites are performed very differently on SSD than they do on a hard drive, and it is common for SSDs to have lower write speeds than reads.
It's actually quite interesting if you're a geek: http://en.wikipedia.org/wiki/Write_amplification
As long as the speeds do match your manufacturer specification for the model (and they do: http://www.samsung.com/us/computer/memory-storage/MZ-7TD250BW ) , there is nothing to be concerned about. -
I'm trying to share a folder between users on a single mac. I want both users to be able to read and write so the folder stays current on both accounts. I put the folder in "shared," set permissions on folder so other user can read and write, enabled file sharing, but can't find the folder on the second user's account. Any help?
Did you log out of one account and into the other or just used Fast user switching?
Is the permissions set to anyone?
When you move data to teh Shared folder is it copied or just moved?
If copied then it's not a folder both can access, just a way station like a USB thumb drive that things are coped too and off of likely.
You can run this #5 on each user account to reset the user permissions once they are taken back out of the Shared folder
Step by Step to fix your Mac -
Can't stop synchronized threads with I/O read and write
I have two synchronized threads which doing read and write from and into a file.
One thread called "reader" which does reading, encoding, etc from a source file and puts its output in a pre-defined variable. Another called "writer" which puts the reader's output into a file ( not the source file ). Both thread will notify each other when they've finished each of their part. It's similiar to CubyHole example of Java Tutorial example from Sun.
But somehow it seems like the threads keep spawning and won't die. Even if the source file has been all read and the data has been fully written, calling interrupt(), return, etc has no effect. The threads will keep running untill System.exit() called.
Is it because the threads were blocked for I/O operation and the only way to kill them is to close the I/O ?
To be honest, it's not only stop the threads that I want to, I also want to somehow pause the threads manually in the middle of the process.
Is it possible ?
Cheers.!!!The example code for the problem using 4 classes called :
- libReadWrite ( class holding methods for aplication operations )
- reader ( thread class responsible for reading data )
- writer ( thread class responsible for writing data )
- myGUI ( user interface class )
All of them written in different file.
// libReadWrite
pubic class libReadWrite {
private boolean dataReady;
private String theData;
//read data
public synchronized void read(String inputFile) {
while (dataReady == true) {
try {
wait();
} catch (InterruptedException ex) {}
RandomAccessFile raf = new RandomAccessFile(inputFile, "r"); // I'm using raf here because there are a lot of seek operations
theData = "whatever"; // final data after several unlist processes
dataReady = true;
notifyAll();
public synchronized void write(String outputFile) {
while (dataReady == false) {
try {
wait();
} catch (InterruptedException ex) {}
DataOutputStream output = new DataOutputStream(new FileOutputStream(outputFile, true));
output.writeBytes(theData);
dataReady = false;
notifyAll();
//Reader
public class reader extends Thread {
private libReadWrite myLib;
private String inputFile;
public reader (libReadWrite myLib, String inputFile) {
this.myLib = myLib;
this.inputFile = inputFile;
public void run() {
while (!isInterrupted()) {
myLib.read(inputFile); <-- this code running within a loop
return;
public class writer extends Thread {
private libReadWrite myLib;
private String outputFile;
public writer (libReadWrite myLib, String outputFile) {
this.myLib = myLib;
this.outputFile = outputFile;
public void run() {
while (!isInterrupted()) {
myLib.write(outputFile); <-- this code running within a loop
try {
sleep(int)(Math.random() + 100);
} catch (InterruptedException ex) {}
return;
//myGUI
public class myGUI extends JFrame {
private libReadWrite lib;
private reader readerRunner;
private writer writerRunner;
//Those private variables initialized when the JFrame open (windowOpened)
libReadWrite lib = new libReadWrite();
reader readerRunner = new reader("inputfile.txt");
writer writerRunner = new writer("outputfile.txt");
//A lot of gui stuffs here but the thing is below. The code is executed from a button actionPerformed
if (button.getText().equals("Run me")) {
readerRunner.start();
writerRunner.start();
button.setText("Stop me");
} else {
readerRunner.interrupt();
writerRunner.interrupt();
} -
Which is better? To wire a URL or a reference into Datasocket read/write?
Does wiring in the reference save processor effort/time? Do I have to close the DS reference before I can do other things to either the same DS connection or other connections? The examples I have looked at tend to use URL's, why is this?
(I am running Labview 7.0 on Windows 2000)I'd like to bring this thread back up because I'm having the same issue as Michael here.....
I'm stumped on a the functionality of the Read/Write mode for the Datasockets Open VI.
I've attached a picture below showing the 2 different methods of
opening Datasocket references....In one case, I use the Read/Write mode
for DS open, in the other case, I use 2 DS opens: One for READ and
another for WRITE. For some reason, only the latter program works
properly (when I open READ and WRITE separately). Why is this?
I
thought that if the READ/WRITE MODE was used, the output reference can
be used with the Datasocket READ and Datasocket WRITE Vi's as shown in
Top Vi of picture. Instead, It seems I'm unable to "change" the state
of the Datasocket tag using the the Top Vi.
FYI: I'm using
DS server manager to create the item. I've also gave proper privileges
to each computer so that they can communicate with the DS server. It
obviously works since using the bottom VI, I get the desired results.
What am i doing wrong? Are my expectations for the Rea/dWrite functionality correct?
Message Edited by RegisPhilbin on 07-15-2005 11:11 AM -
Instrument i/o assistant always generates async methods for read and write!
I am trying to generate VI by instrument i/o assistant, but it generated 'Visa write' and 'Visa read' always in asynchronous mode. Even if I unchecked asynch boxes in MAX->Visa Test Panel.
I need only synchronous mode! And it is very uncovenient after open front panel change Synchronous I/O Mode from Asynchronous to Synchronous!postoroniy_v wrote:
Asynchronous mode does not work for my hardware.
and before Instrument i/o assistant generate diagram I have possibility to check requests and responses to/from my hardware. in this case everything is fine.
after generate does not work.
Is it possible you don't have a sufficient amount of wait time between a VISA Write and VISA read to give the instrument time to receive the communication and turn around a response? Take a look at Basic Serial Read and Write example VI. If you are using the I/O assistant and checking things manually, it will work because there is no way you can generate a Read too fast. It still would take a fraction of second to generate the write and do whatever clicking to generate the read. -
How can i format an external drive so as to read and write from both windows and mac side
i recently bought a macbook pro and used bootcamp so as to be able to run win7 and mac. I now wish to have an external drive so as to backup and tranfer files between the two os's. Specifically to read and write form either windows or mac. How can I do this?
Format it as FAT.
-
Modbus Ethernet read and write to a Eurotherm 6180XIO Modbus server using LV8.2 shared variables
I am having EXTREME difficulty trying to establish communications with a Modbus device using LV8.2 shared variables. The device is a Eurotherm 6180XIO Datalogger configured as a Modbus master. The PC and a cFP-1804 are slaves. All IP addresses are set correctly. This approach using shared variables would seem simple, but I can't find any examples or proper guidance on how to get it working. I am trying to avoid having to mess around with TCP/IP, OPC, or any other old-fashioned method.
I have read many threads on related topics but none directly apply to this situation. I have created a library containing a Modbus I/O server and shared variables bound to read and write holding registers. I have followed all recommended tips for creating such variables but I can neither read or write data. All data types are U16 due to Modbus protocol limitations. I have also applied the LV x10 factor in the most significant digit in the register offset (6 digits instead of 5).
I have a cFP-1804 on the same network which reads into the datalogger OK. The registers I use are 31000 (for CH0 on module 0, 31002 for CH1, etc) and the data can be read as FLOAT32. I have updated the firmwate on the 1804 to the latest level. I cannot even get shared variables to read SGL values. Using registers 301001 for CH0 and 301002 for CH1 I can only read U16 values, and not a 2-word SGL.
Third party Modbus simulation software is able to write to and read from registers very easily, but not LabVIEW.
Some questions are:
- do I use a Modbus master or slave as an I/O server in the library as a target for binding the shared variables?
- is there some other wierd translation in register offsets between LabVIEW and traditional Modbus?
- is this actually possible using shared variables or am I wasting my time?Sending the whole 60-character string using a string or array would be the most efficient. I have tried both methods, and these only cause the datalogger to flag a message log but no text is displayed.
For a string variable, I have used the following binding "My Computer\Modbus Test.lvlib\ModbusServer6180\442305", where ModbusServer6180 is a Modbus I/O server configured with the logger IP address, and 42304 is the register offset at the start of the text block in the logger. I need to write to 30 consecutive registers starting with this one. I am not using buffering and have not enabled single writer.
Can anyone confirm whether this method should work in 8.2?
Does the string need a special termination character? -
Why does this class not read and write at same time???
I had another thread where i was trying to combine two class files together
http://forum.java.sun.com/thread.jspa?threadID=5146796
I managed to do it myself but when i run the file it does not work right. If i write a file then try and open the file it says there are no records in the file, but if i close the gui down and open the file everything get read in as normal can anybody tell me why?
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import bank.BankUI;
import bank.*;
public class testing extends JFrame {
private ObjectOutputStream output;
private BankUI userInterface;
private JButton SaveToFile, SaveAs, Exit; //////////savetofile also saves to store need to split up and have 2 buttons
//private Store store; MIGHT BE SOMETHING TO DO WITH THIS AS I HAD TO COMMENT THIS STORE OUT TO GET IT WORKING AS STORE IS USED BELOW
private Employee record;
//////////////////////////////////////from read
private ObjectInputStream input;
private JButton nextButton, openButton, nextRecordButton ;
private Store store = new Store(100);
private Employee employeeList[] = new Employee[100];
private int count = 0, next = 0;
/////////////////////////////////////////////from read end
// set up GUI
public testing()
super( "Employee Data" ); // appears in top of gui
// create instance of reusable user interface
userInterface = new BankUI( 9 ); // nine textfields
getContentPane().add( userInterface, BorderLayout.CENTER );
// configure button doTask1 for use in this program
SaveAs = userInterface.getSaveAsButton();
SaveAs.setText( "Save as.." );
//////////////////from read
openButton = userInterface.getOpenFileButton();
openButton.setText( "Open File" );
openButton.addActionListener(
// anonymous inner class to handle openButton event
new ActionListener() {
// close file and terminate application
public void actionPerformed( ActionEvent event )
openFile();
} // end anonymous inner class
); // end call to addActionListener
// register window listener for window closing event
addWindowListener(
// anonymous inner class to handle windowClosing event
new WindowAdapter() {
// close file and terminate application
public void windowClosing( WindowEvent event )
if ( input != null )
closeFile();
System.exit( 0 );
} // end anonymous inner class
); // end call to addWindowListener
// get reference to generic task button doTask2 from BankUI
nextButton = userInterface.getDoTask2Button();
nextButton.setText( "Next Record" );
nextButton.setEnabled( false );
// register listener to call readRecord when button pressed
nextButton.addActionListener(
// anonymous inner class to handle nextRecord event
new ActionListener() {
// call readRecord when user clicks nextRecord
public void actionPerformed( ActionEvent event )
readRecord();
} // end anonymous inner class
); // end call to addActionListener
//get reference to generic task button do Task3 from BankUI
// get reference to generic task button doTask3 from BankUI
nextRecordButton = userInterface.getDoTask3Button();
nextRecordButton.setText( "Get Next Record" );
nextRecordButton.setEnabled( false );
// register listener to call readRecord when button pressed
nextRecordButton.addActionListener(
// anonymous inner class to handle nextRecord event
new ActionListener() {
// call readRecord when user clicks nextRecord
public void actionPerformed( ActionEvent event )
getNextRecord();
} // end anonymous inner class
); // end call to addActionListener
///////////from read end
// register listener to call openFile when button pressed
SaveAs.addActionListener(
// anonymous inner class to handle openButton event
new ActionListener() {
// call openFile when button pressed
public void actionPerformed( ActionEvent event )
SaveLocation();
} // end anonymous inner class
); // end call to addActionListener
// configure button doTask2 for use in this program
SaveToFile = userInterface.getSaveStoreToFileButton();
SaveToFile.setText( "Save to store and to file need to split this task up" );
SaveToFile.setEnabled( false ); // disable button
// register listener to call addRecord when button pressed
SaveToFile.addActionListener(
// anonymous inner class to handle enterButton event
new ActionListener() {
// call addRecord when button pressed
public void actionPerformed( ActionEvent event )
addRecord(); // NEED TO SPLIT UP SO DONT DO BOTH
} // end anonymous inner class
); // end call to addActionListener
Exit = userInterface.getExitAndSaveButton();
Exit.setText( "Exit " );
Exit.setEnabled( false ); // disable button
// register listener to call addRecord when button pressed
Exit.addActionListener(
// anonymous inner class to handle enterButton event
new ActionListener() {
// call addRecord when button pressed
public void actionPerformed( ActionEvent event )
addRecord(); // adds record to to file
closeFile(); // closes everything
} // end anonymous inner class
); // end call to addActionListener
// register window listener to handle window closing event
addWindowListener(
// anonymous inner class to handle windowClosing event
new WindowAdapter() {
// add current record in GUI to file, then close file
public void windowClosing( WindowEvent event )
if ( output != null )
addRecord();
closeFile();
} // end anonymous inner class
); // end call to addWindowListener
setSize( 600, 500 );
setVisible( true );
store = new Store(100);
} // end CreateSequentialFile constructor
// allow user to specify file name
////////////////from read
// enable user to select file to open
private void openFile()
// display file dialog so user can select file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
int result = fileChooser.showOpenDialog( this );
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
// obtain selected file
File fileName = fileChooser.getSelectedFile();
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
else {
// open file
try {
input = new ObjectInputStream(
new FileInputStream( fileName ) );
openButton.setEnabled( false );
nextButton.setEnabled( true );
// process exceptions opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE );
} // end else
} // end method openFile
public void readRecord() // need to merger with next record
Employee record;
// input the values from the file
try {
record = ( Employee ) input.readObject();
employeeList[count++]= record;
store.add(record);/////////ADDS record to Store
store.displayAll();
System.out.println("Count is " + store.getCount());
// create array of Strings to display in GUI
String values[] = {
String.valueOf(record.getName()),
String.valueOf(record.getGender()),
String.valueOf( record.getDateOfBirth()),
String.valueOf( record.getID()),
String.valueOf( record.getStartDate()),
String.valueOf( record.getSalary()),
String.valueOf( record.getAddress()),
String.valueOf( record.getNatInsNo()),
String.valueOf( record.getPhone())
// i added all those bits above split onto one line to look neater
// display record contents
userInterface.setFieldValues( values );
// display message when end-of-file reached
catch ( EOFException endOfFileException ) {
nextButton.setEnabled( false );
nextRecordButton.setEnabled( true );
JOptionPane.showMessageDialog( this, "No more records in file",
"End of File", JOptionPane.ERROR_MESSAGE );
// display error message if class is not found
catch ( ClassNotFoundException classNotFoundException ) {
JOptionPane.showMessageDialog( this, "Unable to create object",
"Class Not Found", JOptionPane.ERROR_MESSAGE );
// display error message if cannot read due to problem with file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this,
"Error during read from file",
"Read Error", JOptionPane.ERROR_MESSAGE );
} // end method readRecord
private void getNextRecord()
Employee record = employeeList[next++%count];//cycles throught accounts
//create aray of string to display in GUI
String values[] = {String.valueOf(record.getName()),
String.valueOf(record.getGender()),
String.valueOf( record.getStartDate() ), String.valueOf( record.getAddress()),
String.valueOf( record.getNatInsNo()),
String.valueOf( record.getPhone()),
String.valueOf( record.getID() ),
String.valueOf( record.getDateOfBirth() ),
String.valueOf( record.getSalary() ) };
//display record contents
userInterface.setFieldValues(values);
//display record content
///////////////////////////////////from read end
private void SaveLocation()
// display file dialog, so user can choose file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
int result = fileChooser.showSaveDialog( this );
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
File fileName = fileChooser.getSelectedFile(); // get selected file
// display error if invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
else {
// open file
try {
output = new ObjectOutputStream(
new FileOutputStream( fileName ) );
SaveAs.setEnabled( false );
SaveToFile.setEnabled( true );
Exit.setEnabled( true );
// process exceptions from opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE );
} // end else
} // end method openFile
// close file and terminate application
private void closeFile()
// close file
try {
//you want to cycle through each recordand add them to store here.
int storeSize = store.getCount();
for (int i = 0; i<storeSize;i++)
output.writeObject(store.elementAt(i));
output.close();
input.close();// from read!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
System.exit( 0 );
// process exceptions from closing file
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
System.exit( 1 );
} // end method closeFile
// add record to file
public void addRecord()
int employeeNumber = 0;
String fieldValues[] = userInterface.getFieldValues();
// if account field value is not empty
if ( ! fieldValues[ BankUI.IDNUMBER ].equals( "" ) ) {
// output values to file
try {
employeeNumber = Integer.parseInt(
fieldValues[ BankUI.IDNUMBER ] );
String dob = fieldValues[ BankUI.DOB ];
String[] dateofBirth = dob.split ("-"); // what used to put between number chnage to /
String sDate = fieldValues[ BankUI.START ];
String[] startDate = sDate.split ("-");
String sex = fieldValues[ BankUI.GENDER ];
char gender = (sex.charAt(0)); // check if m or f prob check in employee
if ( employeeNumber >= 0 ) {
/* create new record =String name, char gender, Date dob, String add, String nin, String phone, String id, Date start, float salary*/
record = new Employee(
fieldValues[ BankUI.NAME ],
gender,
new Date( Integer.parseInt(dateofBirth[0]),
Integer.parseInt(dateofBirth[1]),
Integer.parseInt(dateofBirth[2])),
fieldValues[ BankUI.ADDRESS ],
fieldValues[ BankUI.NATINTNO ],
fieldValues[ BankUI.PHONE ],
fieldValues[ BankUI.IDNUMBER ],
new Date( Integer.parseInt(startDate[0]),
Integer.parseInt(startDate[1]),
Integer.parseInt(startDate[2])),
Float.parseFloat( fieldValues[ BankUI.SALARY ] ));
if (!store.isFull())
store.add(record);
else
JOptionPane.showMessageDialog( this, "The Store is full you cannot add\n"+
"anymore employees. \nPlease Save Current File and Create a New File." );
System.out.println("Store full");
store.displayAll();
System.out.println("Count is " + store.getCount());
// output record and flush buffer
//output.writeObject( record );
output.flush();
else
JOptionPane.showMessageDialog( this,
"Account number must be greater than 0",
"Bad account number", JOptionPane.ERROR_MESSAGE );
// clear textfields
userInterface.clearFields();
} // end try
// process invalid account number or balance format
catch ( NumberFormatException formatException ) {
JOptionPane.showMessageDialog( this,
"Bad ID number, Date or Salary", "Invalid Number Format",
JOptionPane.ERROR_MESSAGE );
// process exceptions from file output
catch ( ArrayIndexOutOfBoundsException ArrayException ) {
JOptionPane.showMessageDialog( this, "Error with Start Date or Date of Birth\nPlease enter like: 01-01-2001",
"IO Exception", JOptionPane.ERROR_MESSAGE );
// process exceptions from file output
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error writing to file",
"IO Exception", JOptionPane.ERROR_MESSAGE );
closeFile();
} // end if
} // end method addRecord
public static void main( String args[] )
new testing();
} // end class CreateSequentialFileSure you can read and write at the same time. But normally you would be reading from one place and writing to another place.
I rather regret avoiding the OP's earlier post asking how to combine two classes. I looked at the two classes posted and realized the best thing to do was actually to break them into more classes. But I also realized it was going to be a big job explaining why and how, and I just don't have the patience for that sort of thing.
So now we have a Big Ball Of Tar™ and I feel partly responsible. -
I have the latest Mac Air 13" and I have a Seagate 500MB external hard disk I cant copy or Cut any files on the hard disk and I cant even delete any files. I have the settings as Read and Write in the get info tab. Please helpand also note that my hard drive was formatted on a Windows 7 Laptop.
thats the problem, its in MSDos (Fat) or NTFS for Windows.
Options.....
1. offload all that data on the HD onto your PC, THEN format the HD in EXFAT for use on BOTH PC and Mac for read/write.....then reload all (or as you need) that data back onto the HD
2. get another HD, and format it for Mac OSX extended journaled.
FAT32 (File Allocation Table)
Read/Write FAT32 from both native Windows and native Mac OS X.
Maximum file size: 4GB.
Maximum volume size: 2TB
You can use this format if you share the drive between Mac OS X and Windows computers and have no files larger than 4GB.
NTFS (Windows NT File System)
Read/Write NTFS from native Windows.
Read only NTFS from native Mac OS X
To Read/Write/Format NTFS from Mac OS X, here are some alternatives:
For Mac OS X 10.4 or later (32 or 64-bit), install Paragon (approx $20) (Best Choice for Lion)
Native NTFS support can be enabled in Snow Leopard and Lion, but is not advisable, due to instability.
AirPort Extreme (802.11n) and Time Capsule do not support NTFS
Maximum file size: 16 TB
Maximum volume size: 256TB
You can use this format if you routinely share a drive with multiple Windows systems.
HFS+ ((((MAC FORMAT))) (Hierarchical File System, a.k.a. Mac OS Extended (Journaled) Don't use case-sensitive)
Read/Write HFS+ from native Mac OS X
Required for Time Machine or Carbon Copy Cloner or SuperDuper! backups of Mac internal hard drive.
To Read HFS+ (but not Write) from Windows, Install HFSExplorer
Maximum file size: 8EiB
Maximum volume size: 8EiB
You can use this format if you only use the drive with Mac OS X, or use it for backups of your Mac OS X internal drive, or if you only share it with one Windows PC (with MacDrive installed on the PC)
EXFAT (FAT64) ------Can read/write from both PC and Mac
Supported in Mac OS X only in 10.6.5 or later.
Not all Windows versions support exFAT.
exFAT (Extended File Allocation Table)
AirPort Extreme (802.11n) and Time Capsule do not support exFAT
Maximum file size: 16 EiB
Maximum volume size: 64 ZiB
You can use this format if it is supported by all computers with which you intend to share the drive. See "disadvantages" for details. -
Best Practice to Atomic Read and Write a Field In Database
I am from Java Desktop Application background. May I know what is the best practice in J2EE, to atomic read and write a field in database. Currently, here is what I did
// In Servlet.
synchronized(private_static_final_object)
int counter = read_counter_from_database();
counter++;
write_counter_back_to_database(counter);
}However, I suspect the above method will work all the time.
As my observation is that, if I have several web request at the same time, I am executing code within single instance of servlet, using different thread. The above method shall work, as different thread web request, are all referring to same "private_static_final_object"
However, my guess is "single instance of servlet" is not guarantee. As after some time span, the previous instance of servlet may destroy, with another new instance of servlet being created.
I also came across [http://code.google.com/appengine/docs/java/datastore/transactions.html|http://code.google.com/appengine/docs/java/datastore/transactions.html] in JDO. I am not sure whether they are going to solve the problem.
// In Servlet.
Transaction tx = pm.currentTransaction();
tx.begin();
int counter = read_counter_from_database(); // Line 1
counter++; // Line 2
write_counter_back_to_database(counter); // Line 3
tx.commit();Is the code guarantee only when Thread A finish execute Line 1 till Line 3 atomically, only Thread B can continue to execute Line 1 till Line 3 atomically?
As I do not wish the following situation happen.
(1) Thread A read counter from Database as 0
(2) Thread A increment counter to 1
(3) Thread B read counter from Database as 0
(4) Thread A write counter as 1 to database
(5) Thread B increment counter to 1
(6) Thread B write counter as 1 to database
What I wish is
(1) Thread A read counter from Database as 0
(2) Thread A increment counter to 1
(4) Thread A write counter as 1 to database
(3) Thread B read counter from Database as 1
(5) Thread B increment counter to 2
(6) Thread B write counter as 2 to database
Thanks you.
Edited by: yccheok on Oct 27, 2009 8:39 PMThis is my understanding of the issue (you should research it further on you own to get a better understanding):
I suggest you use local variables (ie, defined within a function), and keep away from static variables. Those local variables are thread safe. If you call functions within functions, its still thread safe. If you read or write to one record in a database using sql, its thread safe (you dont need a transaction). If you read/write to multiple tables and/or records, you probably need a transaction. Servlets are thread safe. You usually dont need the 'synchronized' word anywhere unless you have a function updating/reading a static variable and therefore want to ensure only one user is accessing the static varible at a time. Also do so if you are writing to some resource (such as a file, a variable in applicaton scope, session scope, or resource that everyone uses such as email server). You dont want more than one person at a time to write to it). Note the database is one of of those resources that is handled by transactions rather than the the synchronized keyword (the synchronized keyword is applied to your application only (not other applications that someone is running), whereas the transaction ensures all applications are locked out while you update those records in the database).
By the way, if you have a static variable, you should have one and only one function (synchronized) that updates it that everyone uses. If you have more than one synchronized function, that updates it, its probably not thread safe.
An example of a static variable you would use is a Datasource object (to obtain your database connections). You only need one connection pool in your application and you access it via the datasource variable.
If you're unsure your code is thread safe, you can create two seperate threads that call the same block of functions repeatedly to ensure it works as expected. -
How do I migrate files from an external hard drive created in a Windows OS to a new MAC external drive? I want to read and write these files to the new drive.
LKrzesowski wrote:
How do I migrate files from an external hard drive created in a Windows OS to a new MAC external drive? I want to read and write these files to the new drive.
If all you're trying to do is move the files from the Windows external to the Mac external, you can simply connect them both to the Mac and drag the files from the Windows drive to the Mac drive. If you want to move the files back and forth between them, you'll need to establish the format of the Windows external. Macs can read and write to FAT32 and exFAT (which can handle files larger than 4GB) formatted drives but can only read NTFS formatted drives without additional software. With the Windows drive connected, you can check its format with Disk Utility. -
Distinguishing between CSV and Excel file formats
I am trying to distinguish between CSV and Excel files. Most of the files I need to process are CSV, but some have been opened and re-saved in Excel format. I know about the Excel toolbox available, but haven't used it yet.
I need to be able to open a spreadsheet file regardless of if it is in CSV or Excel format. Any help would be greatly appreciated.
Here are two example files, one CSV and one Excel. Both have .XLS file extensions.
Attachments:
20-4-XLS.xls 21 KB
20-5-CSV.xls 8 KBHi Paul,
I think the matter is not the extention (xls or csv or whatever) but the format of the data written in your file.
To see what I mean, open the xls file you posted with notepad... What does it look like ?
You have tobe sure of the format of the file you want to read so that you can develop an appropriate VI... if you want to be able to read different type of data format, do a test before reading the file and then use an appropriate routine for each format.
Hope this helps you...
BTW, to read the one named CSV, a simple "read from spreadsheet file" VI will do the job
When my feet touch the ground each morning the devil thinks "bloody hell... He's up again!" -
Process using Webservice in Reader and Writer becomes slow while connecting processors
Hi,
I have a process that reads from a web service and writes to a web service. When I try to modify the code(after stopping the running process) by adding new processors or change the current connections, the connecting arrows take forever to connect and sometimes the director hangs for a long time. There is no issue in other processes where I read and write from staged data.
How to overcome this isue?
Appreciate the help!
Regards,
RaviHi Nick,
Thanks for the advice. In the scenario where upgrade is not an option, is there any workaround to this issue?
What I've found is if I strip the next processor of all its connections, then it gets connected to the previous processor pretty quick.
EDQ hangs if the processor has other input/output connections and I try to connect it to another processor)
P1>---<P2> <P3 ---------- P2 to P3 connects fast as P3 is standalone
P1>---<P2> <P3>---<P4> ---------- In this case, when I try to connect P2 to P3, it hangs forever.
I've a complex process and just for adding a few processors in between, I will not be able to connect the rest of the processors all over.
Regards,
Ravi -
Hi everyone,
I just installed a Crucial MX10512 GB SSD into my 2009 Macbook Pro. It's definitely much faster, but the read and write disk speed is around 200 Mb/s for both versus the 300-500 Mb/s that the SSD advertised. Any ideas as to why? And is there anything I can do to make it faster? Before I installed it, it was between 80-90 Mb/s.
Specs:
- currently have about 460 of 511 GB of storage available
- am using 2GB of memory
- running on 10.10.2 Yosemite
Thanks!nataliemint wrote:
Drew, forgive me for being so computer-incompetent but how would I boot from another OS? And shouldn't I be checking the read speeds on my current OS (Yosemite) anyways because I want to know how the SSD is performing on the OS I use? And finally, what kind of resources would it be using that would be slowing down my SSD?
Sorry for all the questions - I'm not a Macbook wiz by any means!
You could make a clone of your internal OS onto an external disk. Hopefully you already have a backup of some form
A clone is a full copy, so you can boot from it. It makes a good backup as well as being useful to test things like this.
Carbon Copy Cloner will make one or you can use Disk Utility to 'restore' your OS from the internal disk to an external one.
Ideally the external disk is a fast disk with a fast 'interface' like Thunderbolt, Firewire 800 or USB3. USB2 can work, but it is slow & may effect the test.
You connect the clone, hold alt at startup & select the external disk in the 'boot manager'. When the Mac is finished booting run the speed tester.
Maybe this one…
https://itunes.apple.com/gb/app/blackmagic-disk-speed-test/id425264550
Test the internal & compare to the previous tests
A running OS will do the following on it's boot disk…
Write/ read cache files from running apps
Write/ read memory to disk if memory is running low
Index new files if content is changing or being updated
Copy files for backing up (Time Machine or any other scheduled tasks)
Networking can also trigger read/ write on the disk too.
You may not have much activity that effects a disk speed test, but you can't really be sure unless that disk is not being used for other tasks.
Disk testing is an art & science in itself, see this if you want to get an idea …
http://macperformanceguide.com/topics/topic-Storage.html
Simply knowing that it's about twice the speed would be enough to cheer me up
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